Loans Receivable - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired loans	$ 0	$ 0
Maturity date	Aug. 31, 2016
Partial repayment of loan on sale of collateralized assets	$ 59,300,000
Net book value of loan after partial repayment	9,313,763,000	9,077,007,000
Risk Rating 4 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Principal Balance of collateralized loan		$ 113,300,000
Net book value of loan after partial repayment	53,600,000
Loan Purchase Commitments [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans originated	861,300,000
Loans funded	$ 586,100,000